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Your IP is detected server-side by PHP. The address shown is what your internet provider assigns to your connection.
::ffff:192.168.1.1).X-Forwarded-For / X-Real-IP are set by load balancers or CDNs (e.g. Cloudflare) and may reveal your original IP.A subnet divides an IP network into smaller parts. The CIDR prefix (e.g. /24) tells you how many bits are used for the network — the rest are host bits.
/24 → 255.255.255.0).192.168.1.10xC0A801013232235777::ffff:192.168.1.1 (RFC 4291)2002:c0a8:0101::/48 (RFC 3056):: omitted::1::ffff:x.x.x.xUnique Local Addresses (ULA) are IPv6 addresses for use within private networks — the IPv6 equivalent of RFC 1918 private addresses (10.x.x.x, 192.168.x.x).
ULAs use the fd00::/8 prefix. The 40-bit Global ID is randomly generated to be statistically unique worldwide, so two networks can be merged without address conflicts — a big advantage over IPv4 private ranges.
RFC 4193 defines ULA. The usable prefix is fd00::/8 (the fc00::/8 half is reserved for future central allocation).
| Bits | Field | Value |
|---|---|---|
| 7 | Prefix | 1111110 |
| 1 | L-bit | 1 (locally assigned) |
| 40 | Global ID | Random (crypto) |
| 16 | Subnet ID | Your choice (0–65535) |
| 64 | Interface ID | EUI-64 or random |
Derived from the MAC address: insert FF:FE in the middle of the 48-bit MAC and flip bit 7. Example: 00:1A:2B:3C:4D:5E → 021a:2bff:fe3c:4d5e.
Enter a start and end IP address to get the minimal list of CIDR blocks that exactly cover the range.
Enter a CIDR block to see the full address range it covers including start, end, and host count.
Any arbitrary IP range can be expressed as a minimal set of CIDR blocks. The algorithm finds the largest aligned block that fits at the current start address, subtracts it, and repeats. A non-power-of-2 range will always require multiple CIDRs.
A CIDR block defines an exact power-of-2 range. A /24 always covers exactly 256 addresses. The network address is the first (all host bits = 0) and the broadcast is the last (all host bits = 1). Usable hosts = total − 2 (for /25 to /30).
| Range | CIDR | Hosts | Type | RFC |
|---|---|---|---|---|
10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | 16,777,214 | Private (Class A) | 1918 |
172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | 1,048,574 | Private (Class B) | 1918 |
192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | 65,534 | Private (Class C) | 1918 |
127.0.0.0 – 127.255.255.255 | 127.0.0.0/8 | – | Loopback | 5735 |
169.254.0.0 – 169.254.255.255 | 169.254.0.0/16 | 65,024 | Link-local (APIPA) | 3927 |
100.64.0.0 – 100.127.255.255 | 100.64.0.0/10 | 4,194,302 | Shared / CGN | 6598 |
192.0.0.0 – 192.0.0.255 | 192.0.0.0/24 | – | IETF Protocol | 6890 |
192.0.2.0 – 192.0.2.255 | 192.0.2.0/24 | – | Documentation (TEST-NET-1) | 5737 |
198.51.100.0 – 198.51.100.255 | 198.51.100.0/24 | – | Documentation (TEST-NET-2) | 5737 |
203.0.113.0 – 203.0.113.255 | 203.0.113.0/24 | – | Documentation (TEST-NET-3) | 5737 |
224.0.0.0 – 239.255.255.255 | 224.0.0.0/4 | – | Multicast | 5771 |
240.0.0.0 – 255.255.255.254 | 240.0.0.0/4 | – | Reserved | 1112 |
255.255.255.255 | 255.255.255.255/32 | – | Broadcast | 919 |
0.0.0.0 – 0.255.255.255 | 0.0.0.0/8 | – | This network | 1122 |
| Prefix | Description | RFC |
|---|---|---|
::1/128 | Loopback Equivalent to 127.0.0.1 | 4291 |
::/128 | Unspecified Equivalent to 0.0.0.0 | 4291 |
::ffff:0:0/96 | IPv4-mapped Embed IPv4 in IPv6 | 4291 |
64:ff9b::/96 | IPv4/IPv6 Translation NAT64 | 6052 |
fc00::/7 | ULA Unique Local (private), usable: fd00::/8 | 4193 |
fe80::/10 | Link-local Not routed, only on local segment | 4291 |
ff00::/8 | Multicast Replaced IPv4 broadcast | 4291 |
2000::/3 | Global Unicast Publicly routable addresses | 4291 |
2001:db8::/32 | Documentation For examples (like 192.0.2.0/24) | 3849 |
2002::/16 | 6to4 Automatic IPv4-compatible tunneling | 3056 |
100::/64 | Discard-Only Black hole routing | 6666 |
| Class | Range | Default Mask | Networks | Hosts/Net | Use |
|---|---|---|---|---|---|
| A | 1.0.0.0 – 126.255.255.255 | /8 | 126 | 16,777,214 | Large networks |
| B | 128.0.0.0 – 191.255.255.255 | /16 | 16,382 | 65,534 | Medium networks |
| C | 192.0.0.0 – 223.255.255.255 | /24 | 2,097,150 | 254 | Small networks |
| D | 224.0.0.0 – 239.255.255.255 | – | – | – | Multicast |
| E | 240.0.0.0 – 255.255.255.255 | – | – | – | Reserved / Experimental |
| CIDR | Subnet Mask | Hosts | Subnets of /24 | Notes |
|---|
IPv4 uses 32-bit addresses (≈4.3 billion). IPv6 uses 128-bit addresses (≈340 undecillion) to solve IPv4 exhaustion. IPv6 has no broadcast — multicast replaces it.
Replaced classful networking. A /24 means 24 bits for the network, 8 for hosts. CIDR enables efficient IP allocation and route aggregation (supernetting).
Allows multiple devices with private IPs to share one public IP. Common in home routers. IPv6 makes NAT unnecessary — every device can have a globally unique address.
Subnet mask: 1s mark network bits (255.255.255.0). Wildcard: 0s mark network bits (0.0.0.255). Wildcards are used in Cisco ACLs and OSPF.
Lets you use different subnet sizes within the same network. E.g. a /30 for point-to-point links (2 hosts) and a /24 for offices (254 hosts).
ISPs assign a /48 or /56 to customers. The customer splits it into /64 subnets — one per LAN segment. Each /64 supports 2⁶⁴ addresses.